1. Technical Field
This invention relates generally to sleeve bearings, and more particularly to sleeve bearing assemblies having a self-lubricating inner journal bearing portion and an outer elastomeric portion for dampening shock loads, such as for use in a suspension system of a vehicle.
2. Related Art
Vehicle suspension components work together to serve a variety of functions, such as maintain proper ride height, maintain wheel alignment, support vehicle weight, maintain the tires in contact with the ground surface, control the vehicle direction of travel, and provide a smooth ride by dampening shock loads. Some of the components are coupled together via sleeve bearings to allow relative movement therebetween. Commonly, the sleeve bearings are fabricated having an outer portion constructed of rubber or urethane and an inner portion constructed of lubricious journal bearing material. The outer portion provides the dampening characteristics desired, while the inner portion reduces friction between the coupled components to allow the relative movement therebetween in use.
It is known to construct sleeve bearing assemblies, such as those described above, by knitting the inner portion first and injection molding the outer portion about the inner portion. The inner portion is known to be knitted from yarn compositions comprising a lubricious yarn material, such as polytetrafluoroethylene (PTFE) fibers, and a structural yarn material, such as polyester fibers. The two yarns are knitted together such that the PTFE follows the pattern of the polyester. Upon knitting the inner portion, it is stretched over an oversized mandrel to remove circumferential slack from the fabric and then located in a mold cavity, whereupon the outer portion is injection molded about the inner portion.
Although sleeve bearing assemblies constructed in accordance with the process described above can be generally effective in use, some improvements can be achieved. For example, the knitted sleeve bearing assemblies utilize an inefficient amount of PTFE in manufacture, given the PTFE follows the knitted pattern of the polyester. As a result, it has been determined that about three turns of PTFE are used in every revolution, and thus, only about 30 percent of the PTFE is actually required to provide a bearing surface, while the remaining 70 percent of the PTFE yarn is not necessary for use as a bearing surface. This ultimately results in cost inefficiencies, given the PTFE is generally the most expensive fiber in the sleeve. Further, the resulting knitted inner portion typically allows the injected molten rubber to penetrate through the knitted yarns and into the bearing surface region of the sleeve. This occurs in part due to the need to stretch the fabric over the mandrel to remove slack from the fabric and because the knitted yarns do not provide a structure tight enough to prevent the rubber from penetrating therethrough. As such, the overall friction reducing effectiveness of the sleeve is reduced. In addition, while performing the injection molding of rubber in the known knitted sleeves, the rubber bonding to the outer surface of the knitted portion can cause the knitted portion to stretch further circumferentially, thereby causing a crease to form in the knitted portion. When this occurs, the resulting product is scrap. Lastly, during the injection molding process, the mandrel becomes increasingly hotter from being exposed to the heat from the molten rubber, thereby presenting an assembly challenge to the operator stretching the inner portion over the mandrel. As such, the operator commonly wears heat resistant gloves, thus, complicating the job.
A sleeve bearing assembly manufactured according to the present invention overcomes or greatly minimizes any limitations of the prior art, such as those described above, for example.